The position of the ink ejection nozzles of the printhead integrated circuit (IC) must be known to accurately print. In known printing cartridges marks referencing the position of the printhead ICs of the cartridge are provided on the body of the cartridge. Communication of these marks with the printer body is used to determine to position of the nozzles. However, referencing the nozzles in this way fails to take account of misalignment and movement of the printhead ICs relative to the cartridge body. In systems requiring low nozzle alignment tolerances, such as color inkjet printers for digital photo printing, such discrepancies can be detrimental to print quality.